Wheel loaders, rigid frame and articulated dump trucks and other machines known in the art are used for moving material from one place to another at a worksite. In loading and moving the work material, these work machines are subjected to varying load conditions and weight distributions caused by the movement and positioning of the components of the machine and the load of material being hauled. In a static or non-moving state, the weight distribution of a work machine, such as for example a wheeled front end loader, is affected by component geometry characteristics, including tire radius and tire pressure, payload mass and position, weights and centers of gravity of the frames, axles, front linkage and implements, as well as optional attachments and their corresponding masses and centers of gravity. The weight distribution is also affected by surface grade and slope that change the orientation of the work machine. In a dynamic state such as when performing work cycles, the weight distribution of the work machine may also be affected by movement of the machine with forward and reverse acceleration and deceleration, at a steering angle and steering rate, and of a front linkage to manipulate the work implement.
In a typical work cycle of a wheel loader, the operator causes the wheel loader to approach a wall or pile of work material, lowers the front linkage and implement, such as a bucket, to ground level and drives the bucket into the work material. As the wheel loader drives into the pile, the wheel loader's forward speed slows down to a stop as the bucket is lifted and tilted to fill the bucket with a load of work material. After sufficiently loading the bucket, the operator reverses the direction of the wheel loader and accelerates out of the pile, typically while turning in the direction that points the front end of the wheel loader toward the destination for unloading the work material, such as at another pile or in the bed of a dump truck. The operator stops the machine, reverses direction and steers and accelerates forward to the dumping location. Where the load of work material is unloaded into a dump truck or hopper, the operator lifts the bucket as the wheel loader is approaching the dump location and stops the wheel loader while tilting the bucket downward to dump the load. The operator will then reverse the direction of the wheel loader and back away from the dump location, turn and acceleration forward toward the work material and repeat the digging process.
In general, work machines such as the described wheel loader are designed to balance the varying weight distributions across the wheels so that the work machine maintains stability during the work cycle. For example, a load of work material at the front of the wheel loader may be balanced by a counterweight in the rear. However, the locations of the centers of gravity of the bucket and linkage as well as the load of material change during the work cycle depending on the position of the linkage arms and the steering position and rate of the wheel loader. Aggressive digging or overloading of the bucket can cause the rear axle to lift partially or completely off of the ground. Quick accelerations, decelerations, steering maneuvers at high speeds or with heavy loads as well as operation on steep grades or slopes can significantly transfer weight to one side or one corner of the machine, thereby reducing the reactant force between the ground and the lightly loaded wheels. In some situations, the torque provided to the lightly loaded wheels may be sufficient to cause the wheels to slip and thereby waste power from the drive train that could be utilized to drive the work machine over the ground.
Mechanical systems have been developed for transferring torque from a sliding wheel to a non-sliding wheel in various vehicles. For example, limited slip differentials include gears that engage when one wheel loses traction and spins to transfer all the torque to the high traction wheel. Electro-mechanical slip limiting systems are known that stop the slipping wheel so that torque can be transferred to the high traction wheel. For example, in some automotive applications having open differentials and anti-lock braking systems, the brakes may be applied to limit or stop the slippage of the low traction wheel so that the open differential transfers the torque to the high traction wheel. The automotive industry has also introduced torque vectoring differentials having the ability to independently vary the torque being sent to each wheel. Automobiles, however, provide relatively consistent weight distributions since the weights of the passengers are in a known location and are relatively small relative to the vehicle weight. In contrast, work machines are subject to loads created by work material having a greater affect on the weight distribution across the wheels of the work machine and that move during the execution of a work cycle performed by the work machine.
One example of a torque distribution strategy is provided in U.K. Patent Appl. No. GB 2 358 163 A, published for Ranson et al. on Jul. 18, 2001, and entitled, “A Motor Vehicle with Controllable Drive Torque Distribution between Each of Its Driven Wheels Responding to Vehicle Load.” The Ranson et al. publication teaches a motor vehicle including load measuring means for each of its wheels and independent drive motors for each of its wheels. A control unit continually monitors the load on each of the wheels and distributes the drive torque accordingly, the wheels with the highest load being supplied with the highest drive torque. The load distribution is also measured before the vehicle starts moving so that the torque distribution can be optimally determined as soon as the vehicle starts off. Measuring loads independently at each wheel of the vehicle likely entails adding components and cost to the vehicle for performing the measurements in work machines designed for hauling loads of work material of varying size and location at a work site.
Therefore, a need exists for an improved method for determining weight distribution and operating conditions for a work machine that is subjected to loads having varying weights and positions while moving work material, and for managing the distribution of torque from a powertrain of the work machine between the wheels of the work machine in response to the determined weight distribution to improve the efficiency of the operation of the work machine, and to maintain stability and safety during use of the work machine.